Along with the popularity of electronic products in people's daily life, the demand for semiconductor devices is increasing. As the design of semiconductor device is directed towards thinness, when the semiconductor device is downsized, the quantity of I/O pins increases, not decreases, making the pitch/width of the wire further decreased and directed towards the design of fine pitch such as 50 μm or even below 35 μm.
However, during the process of bonding the semiconductor device to a package substrate by way of flip-chip assembly, short-circuit may be occurred due to the bridging between two adjacent conductive bumps when the solder is reflowed at a high temperature. In addition, when the solder is not confined by a solder mask which restricts its flow on the wire layer, the solder reflowed at a high temperature may be easily overspread along the wire layer, hence reducing the height between the flipped semiconductor device and the package substrate. As the height is decreased, it will be harder for the underfill layer to be interposed into the gap between the semiconductor device and the package substrate, and the reliability of the package will therefore deteriorate.